In 5-4 decision, majority finds that damages to class not adequately defined.

On the same day that the Supreme Court hears arguments in the Defense of Marriage Act case, the highest court in the land has issued a decision (PDF) in a class-action lawsuit involving a group of Comcast customers in Philadelphia.

The court ruled in favor of Comcast on Wednesday in a 5-4 decision. The petitioners argued that Comcast was monopolizing the Philadelphia market and therefore was charging higher-than-normal prices given its market position. The cable giant has denied the allegations.

The suing customers (who wanted $875 million in damages) said Comcast swapped territories and subscribers with competitors to ensure it could control the market and charge higher prices.

The court denied the petition in a majority opinion written by Justice Antonin Scalia on the grounds that the customers didn’t properly outline an adequate method for issuing damages to the thousands of customers. Legal experts believe that the decision could have further implications for narrowing the definition of similar class action lawsuits in the future.

“For all we know, cable subscribers in Gloucester County may have been overcharged because of petitioners’ alleged elimination of satellite competition (a theory of liability that is not capable of classwide proof),” Justice Scalia wrote. “While subscribers in Camden County may have paid elevated prices because of petitioners’ increased bargaining power vis-à-vis content providers (another theory that is not capable of classwide proof); while yet other subscribers in Montgomery County may have paid rates produced by the combined effects of multi­ple forms of alleged antitrust harm; and so on. The per­mutations involving four theories of liability and 2 million subscribers located in 16 counties are nearly endless.”

However, there are related cases pending in the Chicago and Boston metro areas.